When audiences reflect on Muriel's Wedding, writer-director PJ Hogan's breakthrough 1994 romcom about a love-hungry sad sack who crashes to new lows after tasting the high life, they probably think of exuberant Abba renditions, awkward encounters at weddings and Toni Collette's endearingly dorky performance.

Collecting more than $30m internationally and a Golden Globe nomination for its star, the film – which follows hapless Muriel (Collette) as she experiences popularity for the first time – left an indelible mark on Australian popular culture.

The film's posters depict a jubilant-looking Collette in a wedding dress and a shower of confetti, but audiences who saw an advertisement for a frothy feelgood romance sat down to watch something quite different. Even the film's title seems to be a joke, and a bitter one too: the eponymous wedding marks a low point for an already morally dubious character.

Muriel’s Wedding is a tragicomic portrait of a pathetic woman who, after experiencing a lifetime of degradation, embraces the same kind of vacuousness that defined her as an outcast. The film opens at a wedding, where Muriel catches the bouquet and is taunted by the women around her.

“Throw it again – you’ll never get married,” she’s told. Muriel pleads to her friends that she “can change”, only to be assured that it doesn’t matter: “You’ll still be you.”

The story takes shape when the ugly duckling (sort of) comes good. Muriel happens across some money and discovers a party-going friend named Rhonda (Rachel Griffiths). Soon they’re performing Waterloo on stage; Muriel doesn’t look out of place in a low-lit nightclub; she even has a sex life.

If fate quickly twists in the protagonist's favour – including marriage to a celebrity swimmer and all the attention that comes with it – the pendulum swings back. Rhonda develops cancer and loses her ability to walk. Muriel shelves her as a friend and cosies up to the grown-up mean girls who taunted her. She eventually realises what's right and sets about changing her ways, but the moment of epiphany is far from saccharine and the end of the film points to a future anything but certain, morally or otherwise.

The warmth and heart that creeps into Hogan's screenplay saves Muriel's Wedding from being an exercise in emotional flagellation. If Muriel has a girl-next-door charm, the film has a sort of homely, film-next-door charm: unprepossessing and unpretentious, appealing cross-class and cross-culture.

At the heart of it is a shrewd and deceptively nuanced performance from Collette, then and now a great asset of Australian cinema (she reunited with Hogan for Mental). She wholly inhabits Muriel: her wide-eyed and slightly stupefied look; her Eeyore-like speech; the pathetic way she slumps on her bed and gazes at pictures of other people’s weddings, fantasising of a happiness she neither deserves nor experiences.

Muriel’s Wedding may be remembered as funny, spunky and spirited, and that’s true to a point. It’s also something dark and unusual.